1. Field of the Invention
The present invention relates to connectors that are used in computers, servers, and routers, and more particularly, to a connector that has multiple pairs of signal contacts and is suitable especially for balanced transmission.
2. Description of the Related Art
In recent years, there has been an increasing demand for a large amount of data transmission, as computers and computer networks have been rapidly developed. Especially, video data transmission needs to be carried out at a speed of 1 Gbit/s or higher.
For this type of data transmission, unbalanced transmission methods have been widely employed conventionally, because they are advantageous in terms of costs. By the unbalanced transmission methods, however, it is difficult to avoid adverse influence of noise. Therefore, to carry out high-speed data transmission, it is more preferable to employ a balanced transmission method that can provide resistibility to noise.
FIGS. 1A and 1B illustrate an example of a conventional connector device of a balanced transmission type. The connector device shown in FIG. 1A has a jack connector 1 and a mating plug connector 2.
The jack connector 1 includes pairs of signal contacts 4a and 4b and ground contacts 5a in a housing 3a that is made of an insulating material and is formed longitudinally in the direction of X1-X2 of FIG. 1A.
The housing 3a has a concavity 6a formed longitudinally in the direction of X1-X2. Each pair of signal contacts 4a and 4b has upper ends 4a-1 and 4b-1 protruding in the direction of Z1 from the bottom wall 3a-1 of the housing 3a and extending along the side walls 3a-2 and 3a-3 within the concavity 6a. The signal contacts 4a and 4b in each pair face each other in the direction of Y1-Y2. A ground contact 5a having a fork-like top end 5a-1 is provided between each two neighboring pairs of signal contacts 4a and 4b. 
The lower ends 4a-2, 4b-2, and 5a-2 (not shown) of the signal contacts 4a and 4b and the ground contacts 5a each has a pin-like shape extending in the direction of Z2 and is inserted into a hole 7a formed in a substrate 8a. In this structure, the lower ends 4a-2, 4b-2, and 5a-2 are connected to a printed circuit (not shown) formed on the substrate 8a. 
The plug connector 2 has a shape corresponding to the jack connector 1, and includes pairs of signal contacts 4c and 4d and ground contacts 5b in a housing 3b that is made of an insulating material and is formed longitudinally in the direction of X1-X2 of FIG. 1B.
The housing 3b has protrusions 3b-1 arranged at predetermined intervals in the direction of X1-X2 within a concavity 6b. Each pair of signal contacts 4c and 4d has pin-like upper ends 4c-1 and 4d-1 protruding from the bottom wall 3b-2 of the housing 3b and extending along the both sides of each corresponding protrusion 3b-1 in the direction of Y1-Y2. A ground contact 5b having a flat top end 5b-1 is provided between each two neighboring pairs of signal contacts 4c and 4d. 
The lower ends 4c-2, 4d-2, and 5b-2 (not shown) of the signal contacts 4c and 4d and the ground contacts 5b each has a tongue-like top end that is bent in the direction of Y1-Y2 of FIG. 1B. This tongue-like top end is fixed to a pad (not shown) formed on a substrate 8b, and is thus connected to a printed circuit (not shown) formed on the substrate 8b. 
The plug connector 2 is connected to the jack connector 1, so that the signal contacts 4a and 4b are brought into contact with the signal contacts 4c and 4d, and that the ground contacts 5a sandwich the corresponding ground contacts 5b. Thus, the signal contacts and the ground contacts are electrically connected to one another. If a positive signal is transmitted through the signal contacts 4a and 4c in this case, a negative signal is transmitted through the signal contacts 4b and 4d. 
With the above conventional connector device, however, there is a problem that desired balanced transmission cannot be carried out, because the mating lower ends 4c-2 and 4d-2 extend in the opposite directions and cannot establish preferable coupling.
Meanwhile, a wiring pattern may be formed on the substrates, so that one ends of the wires extend from either one side (the Y1 side or the Y2 side in FIG. 1B) of the longitudinal walls of the housings 3a and 3b, while the other ends of the wires are connected to a terminal unit or the like provided at a predetermined location on a line extending from the one side. In such a case, however, wires of uniform lengths cannot be provided between the terminal unit and each pair of signal contacts, because one of the signal contacts in each pair is located farther away from the terminal unit. The variation of the wire lengths causes phase difference between signals subject to balanced transmission through each pair of signal contacts. The phase difference results in noise, and makes the characteristic impedance unstable.
To prevent the noise generation and stabilize the characteristic impedance, the lengths of wires to be connected to the signal contacts closer to the terminal unit are adjusted to the same lengths as the lengths of the wires to be connected to the signal contacts farther from the terminal unit.
However, the employment of wires at the unnecessary locations, i.e., the excessive lengths of wires, only complicates the wiring design and the wiring operation for the substrates.